Packer is controlled using a command-line interface. All interaction with Packer
is done via the packer tool. Like many other command-line tools, the packer
tool takes a subcommand to execute, and that subcommand may have additional
options as well. Subcommands are executed with packer SUBCOMMAND, where
"SUBCOMMAND" is the actual command you wish to execute.

If you run packer by itself, help will be displayed showing all available
subcommands and a brief synopsis of what they do. In addition to this, you can
run any packer command with the -h flag to output more detailed help for a
specific subcommand.

In addition to the documentation available on the command-line, each command is
documented on this website. You can find the documentation for a specific
subcommand using the navigation to the left.

By default, the output of Packer is very human-readable. It uses nice
formatting, spacing, and colors in order to make Packer a pleasure to use.
However, Packer was built with automation in mind. To that end, Packer supports
a fully machine-readable output setting, allowing you to use Packer in automated
environments.

Because the machine-readable output format was made with Unix tools in mind, it
is awk/sed/grep/etc. friendly and provides a familiar interface without
requiring you to learn a new format.

The machine-readable output format can be enabled by passing the
-machine-readable flag to any Packer command. This immediately enables all
output to become machine-readable on stdout. Logging, if enabled, continues to
appear on stderr. An example of the output is shown below:

The machine readable format is a line-oriented, comma-delimited text format.
This makes it more convenient to parse using standard Unix tools such as awk or
grep in addition to full programming languages like Ruby or Python.

target is the target of the following output. This is empty if the message
is related to Packer globally. Otherwise, this is generally a build name so
you can relate output to a specific build while parallel builds are running.

type is the type of machine-readable message being outputted. There are a
set of standard types which are covered later, but each component of Packer
(builders, provisioners, etc.) may output their own custom types as well,
allowing the machine-readable output to be infinitely flexible.

data is zero or more comma-separated values associated with the prior type.
The exact amount and meaning of this data is type-dependent, so you must read
the documentation associated with the type to understand fully.

Within the format, if data contains a comma, it is replaced with
%!(PACKER_COMMA). This was preferred over an escape character such as \'
because it is more friendly to tools like awk.

Newlines within the format are replaced with their respective standard escape
sequence. Newlines become a literal \n within the output. Carriage returns
become a literal \r.

The set of machine-readable message types can be found in the
machine-readable format complete
documentation section. This section contains documentation on all the message
types exposed by Packer core as well as all the components that ship with
Packer by default.